Measuring and control apparatus



July 13, 1943. w; P, W LLS 2,323,885

MEASURING AND CONTROL API ARATUS Original Filed June 22, 1938 2 m INVENTOR" D I T 97 3 WALTER P. WlL-LS 83 I05 no! 64 v mfg ATTOR EY.

Patented July 13, 1943 MEASURING AND CONTROL APPARATUS Walter P. Wills, Philadelphia, Pa" assignor to The Brown Instrument Company, Philadelphia, Pa.. a corporation of Pennsylvania Original application June 22, 1938, Serial No. 215,127.- Divided and this application May 14, 1941, Serial No. 393.469

Claims.

This invention relates to electronic control circuits.

The present invention is a division of my prior application Serial No. 215,127, filed June 22, 1938, now Patent No. 2,289,947, and said prior application was a continuation in part of my application Serial No. 159,875, filed August 19, 1937, now Patent No. 2,256,304. Each of these prior applications disclose various arrangements of an electrical control instrumentality of the kind which may be used to control the application of a quantity in response to the fluctuations of a variable condition to maintain the condition constant.

A specific object of the present invention is to provide an electronic control circuit which is especially adapted for use in a system of the type referred to, and is relativelysimple in construction and may be operated from a commercial alternating current supply source without the use of transformers and power rectifiers.

A more specific object of the present invention is to provide an electronic control circuit which is sensitively responsive to minute alternating voltages and will amplify and translate all frequencies over a Wide range of frequencies into a direct current potential which may b employed to effect a control operation.

A still more specific object of the present invention is to provide an electronic control circuit of the type referred to above in which automatic compensation for fluctuations in the voltage of the alternating current supply source is had.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be made to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawing:

Fig. 1 is a diagrammatic view illustrating one embodiment of the invention as adapted for use in controll ng the temperature of a furnace;

F'g'. 2 is a perspective view of a portion of the arrangement of Fig. 1 which is employed for set-- ting the mechanical zero of the galvanometer employed in that arrangement;

Fig. 3 illustrates a modification of the amplifier shown in Fig. 1;

Fig. 4 illustrates a modification of the arrangement disclosed in Fig. 1 including means for modulating the heat input to the furnace; and

Figs. 5 and 6 illustrate modification of a portion of the arrangement of Fig. 4.

In Fig. 1 of the drawing, I have illustrated, more or less diagrammatically, a furnace or other compartment to be heated at l in which an electrical heating element 2 is arranged and adapted to be supplied with energizing current from supply conductors 3 and 4. A thermocouple 5, which is sensitively responsive to variations in temperature, is mounted in the furnace l and has its terminals connected by conductors 8 and 7 to the terminals of a deflectional potentiometric measuring network 8 at a point remote from the furnace l.

The potentiometer network 8 may be of any suitable type such as the Brown potentiometer circuit disclosed in the Harrison Patent 1,898,124 issued February 21, 1933, and for the present purposes it is sufficient to note that the potentiometer circuit 8 includes a circuit branch comprising the thermocouple 6, an opposing circuit branch including a source of known potential, such as a battery 9 and a pair of resistors l0 and Ii, a variable portion of which may be connected into the opposed branches by means of a sliding contact I! whereby the respective effects of the variable and the known sources are made equal and opposite. Differences in the variable and known sources of potential are adapted to be detected by a galvanometer iii, the moving coil i i of which is connected in the circuit branch including the thermocouple 5, so that when the variable and known sources of potential are equal and opposite the galvanometer moving coil will be rendered undefiected when the circuit is balanced for a predetermined value of the E. M. F. of the thermocouple with the contact l2 in acorresponding position along the slidewire resistors ill and ii.

A illustrated the moving coil it of galvanometer I3 is connected in the conductor 8 by means of slip rings l5 and I6, and a pick-up coil i1 is connected to the 'pivot of th galvanometer moving coil. The pick-up coil I1 is positioned between the poles of a field structure i9 having a field winding l9 which is adapted to be energized from the' alternating current supply lines L and I and is preferably, although not necessarily, so arranged that when the galvanometer is in its undefiected position the pick-up coil will be slightly in inductiv relation with the alternating magnetic field set up by the field structure. The extent to which the pick-up coil I1 is in inductive relation with this alternating magnetic field and the manner in which the adjustment may be effected is described hereinafter.

For facilitating the adjustment of the instrument to control the'temperature of the furnace l at the desired value the potentiometer sliding contact l2 may be mounted on a contact arm 29 which desirably is arranged in cooperative relation with a suitably calibrated scale 2| and is adapted to be rotated to any desired position along the scale by a knob 22.

When the temperatur of the furnace I varies in one direction or the other from the desired value, the generated thermocouple voltage will change to a corresponding extent and as a result the thermocouple and opposed potentiometer voltages will become unequal in alue and current will flow in one direction or the other through the galvanometer moving coil l4. The gaivanometer moving coil thus energized will defiect in a corresponding direction and rotate the pick-up coil I! to a new position between the poles of the field structure l8.

The alternating voltage induced in the pick-up coil ll from the field created by the winding i9 is connected by slip rings 23 and 24 and conductors 25 and 26 to the input terminals of an electronic amplifier 21 which is employed to amplify the induced voltage and the amplified quantity is employed to control the energization of a suitable relay 28 into its open or closed position.

The amplifier 21 illustrated is especially desirable in a system where simplicity, compactness and ease of construction are essential features for, as will be described it may be operated directly from the alternating current supply conductors L and L and does not require the use of power rectifiers or transformers. As shown, the conductor 25 is connected to the control grid 33 of an electronic valve 29 and the conductor 26 is connected to the cathode 3! thereof. The valve 29 is a heater type triode and includes an anode 30, the cathode 3|, a heater filament 32, and the control grid 33. The heater filament 32 is adapted to receive energizing current from the alternating current supply conductors L and L" and is connected in a series circuit thereacross which includes the heater filaments 31 and 43 of a pair of electronic valves 34 and 40 and a pair of resistors 48 and 41. It is noted that this circuit in effect comprises a voltage divider from which various potentials may be tapped to supply energizing voltages to the valves 34 and 49.

The valve 34 is a heater type duplex-diodetriode and includes an anode 35, a cathode 36, the heater filament 31, a control grid 38 and a pair of diode plates 39, and the valve 49 is a tetrode preferably of the type known commercially as beam power amplifier tubes and includes an anode 4i, a cathode 42, the heater filament 43, a control grlde 44, and a screen grid 45.

As will become apparent the valve 34 is employed to supply directcurrent voltage to the anode circuit of valve 29 and also to further amplify the amplified quantity of the volt ge induced in the pilot coil I! which is impressed upon the input circuit thereof by the valve 29. Anode voltage is supplied the valve 29 through a circuit which utilizes the rectifying action of the diode plates 39 of valve 34 and which may be traced from the supply conductor L to a conductor 48, conductor 49, heater filament 31, a conductor 59. resistor .41, a conductor ll. the diode plates 39, cathode 33, and a conductor 92 to one terminal of a condenser 33 which constitutes the positive side of a half wave rectifying unit. The condenser 53 has its negative terminal connected by a conductor 54 to the supply conductor L and operates to smooth out ripples in the rectified current flow through the circuit including the diode plates 39 and cathode 39 which impresses a definite constant voltage across its terminals. As illustrated. the anode 39 of valve 29 is connected to the positive side of condenser 53 through a resistor 55 and the oathode 3i is connected to the negative side thereof.

In order to limit the flow of ripple current through the valve 29 to a negligible value and to permit the use of a small filtering condenser 53, the valve 29 is preferably operated with the oathode 3l virtually cold and with a relatively low voltage on the anode circuit. The temperature of the cathode 3! may conveniently be kept at a low value by shunting the heater filament with a resistor 53 so that the filament heating current will be small, and it will be apparent the potential on the anode 30 may be adjusted to a desirable value by properly proportioning resistor 49. Thus, by so adjusting the anode to cathode resistance of valve 29, it will be readily apparent that the discharge of current through the valve 29 by the condenser 53, during the half cycles when the diode plates 39 are negative, may be reduced to a negligible value and the voltage maintained on the anode 39 may be maintained at a substantially constant value. It is noted that this method of increasing the anode to cathode impedance of valve 29 is advantageous over the well known method of applying a negative bias to the control grid in that the valve may be operated over an optimum portion of its plate current grid voltage characteristic whereas such operation is not possible when the control grid is,

negatively biased.

when the voltage impressed on the input circuit of valve 29 is zero, that is when the pick-up coil i1 is in zero inductive relation with the magnetic field set up in the field structure i8, the valve 29 will conduct a steady flow of current of predetermined value, and accordingly a substantially constant potential drop will be maintained across the resistor 55. When the pick-up coil is deflected in one direction or the other from its neutral position, however, it is noted an alternating voltage in phase with or out of phase with the line voltage will be impressed on the input circuit of valve 29, and the latter will then be alternately rendered more conductive and less conductive resulting in a pulsating direct current fiow through resistor 55 and thereby in a corre- :ponding pulsating potential drop across the lat- The positive end of resistor 55 is connected to the cathode 3B of valve 34 and a connection is also provided between this end of resistor 55 and the control grid 38 which includes a resistor 51. As shown a condenser 53 is connected in shunt to the resistors 55 and 51 and it will be apparent that when a steady flow of current is conducted by valve 29 a charge will be stored on the concharge and discharge through the resistor 51 to produce a'iluctuating potential drop across the latter, and it will be noted this potential drop will be impressed on the input circuit of valve 34.

Anode voltage is supplied the valve 34 directly from the alternating current supply conductors L and L through a circuit which may be traced from the supply conductor L conductor 48, con-v ductor 49, heater filament 31 of valve 34, conductor 66, a conductor 59 in which a resistor 66 is inserted, anode 36, cathode 36, and conductor 62 to the positive terminal of condenser 63. Thus, the anode circuit of valve 34 is completed through the parallel arrangement consisting of the anode circuit of the valve 29 and the condenser 63, and it is noted the magnitude or the pulsating current conducted by valve 34 is adapted to be varied in accordanc with variations in the conductivity of valve 29.

In order to render negligible the efiect of variations in the anode current conducted by valve 34 on the potential maintained on the anod circuit of valve 29, the'current conducted by the diode section of valve 34 should preferably be made many times as large as the current conducted by the anode circuit thereof. Or in other words the diode plates 33 of valve 34 should be connected to a point on the voltage divider of such potential that the potential of the cathode 36 will be determined primarily by the current conducted in the circuit including the diode plates 39 and the cathode 36.

The obvious manner of rendering the current conducted by the diode section of the valve predominant in determining the potential of cathode 36 would .be to connect the diode plates '39 directly to the supply conductor L but it is noted that if this is done the voltage available for the anode circuit of valve 34 will beinsuilicient. Thus, the diode plates 39 must be connected to a point on the voltage divider of such potential that the current conducted, by the diodes will be predominant in determining the potential of the cathode 36 and in addition that there will be sufficient voltage available for the anode section of the valve 34.

When a fluctuating potential is impressed on the input circuit of valve 34. this valve will be rendered less conductive or more conductive durtive depending upon whether the voltage impressed on the input circuit thereof is in phase or I displaced 180 in phase with the alternating voltage applied to the anode, and accordinglyv the current flow through resistor 66 will be varied to a corresponding extent. In order to smooth out the pulsating current flow through resistor 66 a condenser 6| is connected thereacross, and as will be apparent a potential drop will then be produced across resistor 66 which will gradually rise when an alternating potential in phase with the supply line voltage is impressed onfithe input circuit of valve 34 until a condition of equilibrium is reached and which will gradually fall to a lower value when an alternating voltage 180 out of phase with the supply line voltage is impressed constants may be as follows:

on the input circuit of valve 34. Thus, a negative potential is built up on the anode 35 which is adaptedto be varied as the pick-up coil H deflects in one direction or the other from its normally balanced position and as will become apparent this negative potential may desirably I Y be employed to control the conductivity of valve 46.

voltage of the supply conductors is 110 volts, the valve 29 may be of a type known commercially as a 6165 type, the valve 34 may be a type 6Q7, the valve 46 may be a type 25L6, and correspondingly suitable values for the various circuit 7 Value Part As illustrated the anode circuit of valve 46 is connected in an inverted position across the alternating supp y conductors L and L with revspect to the manner of connection of the valve 34 thereacrossso that the'valve 46 will be nonconductive during the half cycles when the valve 34 i conductive, and conductive when the valve 34 is nonconductive. Due to the action of condenser- 6i, however, the potential drop across resistor 66 will persist during the half cycles when the valve 34 is non-conductive and may,

therefore, be employed to control the conductivity of valve 46 which is conductive during these halt cycles. As shown the negative end of resistor 66 is connected by a conductor 62 to the control grid 44 of valve. 46 and the positive end of resistor 66 is connected by means of conductor 56, the heater filament 31 of valve 34, and conductors 43 and 48 to the cathode 42 so that the potential drop across resistor 66 will be impressed on the input circuit of valve 46.

'Anode voltage is supplied the valve 46 through a circuit which may be traced from the supply conductor L a conductor 63 in which a milliammeter 64 and the relay 26 are inserted, the anode 4|, and cathode 42 to the supply conductor L The screen grid 45is desirably maintained at a potential which is somewhat lower than the potential applied the anode 4i and may be'connected to the point of connection of resistors 46 and 41.

Thus the valve 46 is adapted to be alternately rendered conductive and non-conductive and-the amplitude of the pulsating current conducted therebyis adapted to be controlled in accordance with the direct current potential drop across resistor 66. In order to smooth out the pulsating current flow through the relay 28 and the milliammeter 64 to thereby prevent chattering of the relay and to facilitate readingof the milliammeter, a condenser 65 is preferably connected across these units.

It is noted that when the above values for the various circuit'components are used 'and suitably matched electronic valves are employed; an automatic compensation for line voltage fluctuations By way or illustration it is noted that when the should vary. Such automatic compensation may be obtained, when unmatched electronic valves are employed, by suitable adjustment of the values of the various circuit components, particularly adjustment of the resistance of resistor 60 and relay 28 and the point of connection of screen grid 45 of valve 40 along resistors 46 and 41.

In the circuit arrangement illustrated, a line voltage change tends to vary the anode current of valve 40 in much the same manner as that current is varied by defiection of pilot coil II from its normal position, but such change in line voltage may be precisely compensated for in a manner to be explained. This compensating action is obtained by virtue of the fact that if the line voltage should change, increase, for example, the conductivity of valve 34 will increase to produce a greater voltage drop across resistor 60, and this increase in biasing potential across the latter will exactly offset the tendency of valve 40 to conduct a larger current as a result of said line voltage increase. I have found, in practice, that when the electronic valve characteristics and the circuit constants have been suitably proportioned, the line voltage may vary as much as 20% in either direction from an intermediate normal value, for which the apparatus is designed, without resulting in significant change in the anode current conducted by valve 40.

An armature 86, whichis shown pivoted at a point 67 and gravity or spring biased for rotation in a, counterclockwise direction into engagement with a stop 68, is arranged in cooperative relation with the relay 28 and is adapted to be rotated in a clockwise direction into engagement with the relay core when the relay is energized. The armature 66 may be formed in the shape of a right angle and the point 81 at which it is pivoted may conveniently be at the bend. One arm is directed in an upward direction and is adapted to move between the stop 68 and the relay 28, and the other arm which is adapted to be moved about a horizontal position carries a. mercury switch 69. The mercury switch 69 includes contacts which are adapted to be closed when the armature 66 is in its extreme clockwise position and to be opened when the armature is in its extreme counter-clockwise position as shown;

As illustrated the contacts 10 are connected in a circuit including the heating resistor 2 and the power supply conductors 3' and 4 so that when the relay 28 is energized the mercury switch 89 will be actuated into its closed position to close an energizing circuit to the resistor 2. Thus, as the temperature of the furnace I rises above or falls below a predetermined value at which it is desired to control the temperature, the mercury switch 69 will be actuated to its open and closed position accordingly to thereby cut off or supply more heat to the furnace.

As was mentioned hereinbefore, I contemplate two modes of operation for my control system. In accordance with one method I contemplate operat on in which the pick-up coil i1 is normally slightly in inductive relation with the magnetic field set up in the field structure l8 and in which the phase of the induced voltage is not changed as the relay 28 is actuated to its open and closed position, but only the amplitude of the induced voltage is varied. By so operating my control system it is noted the effects of extraneous voltages which may be induced in the pick-up coil in the normal operating position of the latter may be minimized, and in addition the relative adjustment of the pick-up coil I1 and field structure l8 required may desirably be employed to cause positive de-energization of the relay 28 upon de-energization of the galvanometer moving coil I4, which de-energlzation may be caused by thermocouple fallure, for example. This latter feature will be described more in detail hereinafter.

When extraneous voltages are induced in the pick-up coil in the normal operating position of the latter, and the instrument is adjusted asit would necessarily have to be adjusted to be unresponsive to the currents produced by the extraneous voltages, a dead spot will be introduced into the operation of the instrument. Such extraneous voltages may be due to the presence of magnetic material external to the field structure I8 which may cause distortion of the magnetic field or may be due to non-uniformity of the field structure itself. As will be readily appreciated it is extremely dimcult to construct a field structure in which the ma netic field will be exactly uniform. When the magnetic field is not uniform and the pick-up coil is in a position in which the induced voltage therein should be zero, the latter may have induced therein voltages of harmonic frequencies which are unstable and may operate to energize the relay 28 into its. closed position. It is noted the amplifier 2! does not distinguish between frequencies as does the usual amplifier and will amplify and translate all frequencies over a wide range into a direct current potential which may be employed to control the conductivity of valve 48.

As will be apparent, when the pick-up coil I1 is deflected in one direction from the position in which it is in zero inductive relation with the fundamental frequency of the alternating magnetic field set up in the field structure l8, a voltage of one phase will be induced in the pick-up coil to cause actuation of the relay 28 in one direction and when the pick-up coil is deflected in the opposite direction a voltage of the opposite phase will be induced therein to cause actuation of the relay 28 in the opposite direction. If, however, transient induced voltages opposing either or both of the purposely induced voltages appear, the instrument will be prevented to the extent of the character and the magnitude of the transient voltage from effecting the desired actions of relay 28. If the transients are known and constant, the instrument may be so adjusted as to compensate for them, but in any case must be made insensitive to them. Thus a dead spot will be introduced into the movement of the pick-up coil and the system will be rendered insensitive to a corresponding extent.

Such a dead spot is undesirable, however, in a controller of the type disclosed, and I prefer to so operate the system that the phase of the purposely induced voltage in the pick-up coil does not change as the relay 28 is actuated from its open to its closed position, but only the amplitude of the induced voltage is changed. By adjusting the amplitude of the induced voltage in the pick-up coil, when the galvanometer moving coil is in its position of electrical balance, to a value equal to or greater than the transient induced voltages in the pick-up coil, it will be apparent that the transient voltages will have no effect on the operation of the system. Or in other words, when the pick-up coil is normally in inductive relationship with the fundamental frequency of the alternating magnetic field set up in the field structure l8, the effect of the transient voltages induced in the pick-up coil wilL be minimized and more stable operation of the instrument may be obtained.

As will be apparent, in control systems of this type it isdesirable that upon a thermocouple or amplifier valve burnout, or other failure of the control apparatus, occurring when the relay 28 is in its closed position that the apparatus shall fail safe," that is any one of the failures enumerated shall result in actuation of the relay 28 to its open position to thereby shut off the supply of heat tothe furnace. Injury to the furnace and its contents which would ordinarily result before the attendant in charge would detect the failure may thus be prevented.

With the apparatus described it will be noted that burnout of any one of the heater filaments of the amplifier valves will result in de-ener lzation of the amplifier. To guard against the objectionable possibility of injury to the furnace and its contents upon thermocouple failure the various components of the apparatus should be so adjusted that when the thermocouple circuit is open circuited, the relay 28 will be de-energized. It is noted this effect may be obtained by so adjusting the instrument that when the potentiometric network 8 is balanced the relay 28 will be de-energized. Thus, when the galvanometer moving coil is de-energized, the relay 28 will be actuated to its open osition if it is not already in this position and the supply of heat to the furnace will be shut off. It is noted, however, that it is desirable in a system of this type to provide means for positively causing de-energization of the relay 28 upon thermocouple failure instead of relying solely on the normal adjustment of the system. As mentioned hereinbefore, this end may be attained in my control system by the same adjustment which is effective to minimize the effects of extraneous voltages induced in the pickup coil ii.

For example, by adjusting the instrument so that when the temperature is at the desired value the galvanometer moving coil M will be slightly out of its mechanical zero position, that is, the position which the galvanometer will assume when its terminals are shorted or open circuited, it will be noted that thermocouple failure will result in movement of the galvanometer moving coil to its mechanical zero position. The pick-up coil I! may be so adjusted with respect to the galvanometer moving coil that in normal operation when the temperature is at the controlled value it will be slightly in inductive relation with the field structure i8, the phase of the induced voltage being such that a positive potential will be impressed on the control grid 33 of valve 28 during the half cycles when the anode 35 of valve 84 is positive, and upon thermocouple burnout the resulting movement of the galvanometer movin coil into its position of mechanical zero adjustment will rotate the pick-up coil i! into zero inductive relation with the field structure i8, or into a position in which the voltage induced therein will be of the opposite phase to thereby cause positive de-energization of the relay 28.

In accordance with the second method of operation of my control system which I contemplate, the pick-up coil is normally maintained in a position of zero inductive relation with the field structure l8 and adapted to have voltages of opposite phases induced therein as it is deflected in one direction or the other from this normal position. It will be apparent that by providing a field structure" especially designed and. magnetically shielded the transient'voltages induced in the pick-up coil I! may be minimized and consequently the "dead spot referred to hereinbefore may be reduced to a minimum.

Thus, with either method of operation, the sensitivity of the instrument may be so adjusted that when the galvanometer moving coil is in its position of electrical balance the flow of current through the relay 28 will be insufllcient to actii ate the relay to closed position, but on a slight change in temperature and consequent deflection oi the galvanometer moving coil the energizing current to the relay will be increased sufliciently to actuate itto closed position. v

This adjustment may conveniently be effected by the arrangement illustrated in detail in Fig. 2 which as shown includes a screw shaft H and an associated lever 12. One end of the lever 12 is rigid with a stud 18 which is mounted for rotation. on the end of a horizontally projecting arm of a stationary bracket 14, and the other end of the lever is adapted to slide in a groove on the screw shaft H so that when. the latter is rotated the lever 12 will be rotated about its pivot thereby rotating the stud 13. A flexible U-shaped member 15 is rigidly connected at the end of one arm to the end of a lever 16 the other end of which is rigid with the stud I3. The lever 16 extends back along the projecting arm of bracket 14 and, when the lever 12 is in a mid position along the screw shaft II, the lever 16 will be directly above and parallel to the projecting arm of the bracket, and is adapted to be moved out of this parallel position when the screw shaft is rotated. The flexible member 15 is so arranged with respect to 'the lever 16 that one arm is directly above and parallel to the latter and extends beyond the stud J3, and the other arm is directly below and parallel to the lever I6. The galvanometer suspension wire is fixed to the latter arm of member 15 at a point which is on the axis of rotation of the stud so that when the screw shaft 1| is rotated the galvanometer moving coil l4 and the pilot coil I! will be rotated with respect to their respective fleld structures.

It is noted this galvanometer mechanical zero adjustment for adjusting the sensitivity and helping the instrument to fail safe may be facilitated when the milliammeter 64 is employed in conjunction therewith for indicating when the adjustment is at the desired value. For example, by short circuiting the terminals of the galvanometer moving coil l4, as by a switch 11, the

screw shaft ll may be rotated until the anode current flow through valve 40 is a desirable value, and by providing a milliammeter of suitable value, this current flow may desirably cause defiection of its pointer half way up scale. Move-- ment of the galvanometer and pilot coil from this mechanically fixed position will then result in the flow of more or less current through the milliammeter 64 and thereby in deflection of its pointer in one direction or the other from the mid-position. Thus, by closing the switch 11, a rapid check may be made as to the mechanical zero adjustment of the galvanometer and if the adjustment is not correct, a correct adjustment may-readily be effected by rotation of the screw shaft H. As shown, a projection may desirably be provided in one end of the latter for facilitating the rotation thereof, as for example; by a suitable key adapted to engage that projection.

As was noted the pulsating anode current conducted by valve 48 is adapted to be controlled in accordance with the magnitude of the direct current; potential maintained across resistor 88 and this potential in turn is adapted to be controlled in accordance with the magnitude of the alternating voltage impressed upon the input circuit of valve 29 by the pilot coil I'I. Moreover, since the resistor 88 is shunted by the condenser 6i, it will become apparent that sudden changes in the alternating voltage induced in the pilot coil I1 will change only slightly the direct current potential drop across resistor 68. Thus, if the galvanometer moving coil i4 and the pilot coil I! are deflected from their neutral position as a result of jarring or vibration, the resulting transltory'voltage induced in the pilot coil Il will produce only a slight change in the direct current potential drop across resistor 88 which will ordinarily be ineifective to actuate the relay armature 88 into its closed position. If the voltage induced in the pilot coil should persist, however, the potential drop across resistor 68 will be changed sufliciently to cause the relay armature to be actuated into its closed position, but it is noted that as soon as the vibration ceases, the galvanometer and pilot coils will return to their neutral positions and the relay armature will be permitted to assume its open position.

In Fig. 3 I have illustrated, more or less diagrammatically, a modification of the amplifier arrangement disclosed in Fig. 1 in which an additional stage of amplification is provided and in which the rectifier unit may be connected directly across the supply conductors L and L As illustrated .the terminals of the picl -up coil I I (not shown in this arrangement) are connected by conductors 25 and 28 to the inputcircult of one triode section of an electronic valve I8 which may desirably be a twin amplifier type including two triodes in one envelope. This triode section includes an anode 19, a cathode.

88, a heater filament 8|, and a control grid 82 and the output circuit' thereof is resistancecapacity coupled by a resistance 83 and a condenser 83' to the input circuit of the second triode section in the envelope. For convenience in describing the circuit connections, the first mentioned triode will be referred to hereinafter as the triode A and the second mentioned triode will be referred to as the triode B.

The triode B includes an anode 84, a cathode 85, a heater filament 88, and a control grid 81. Energizing current is supplied the heater filaments 8i and 88 through a circuit which includes the heater filaments 9I and 95 of a twin type amplifier valve 88, and the heater filament 43 of valve 48, andmay be traced fromthe supply conductor L to the heater filaments BI and 88, a conductor 91, heater filaments 9I and 95 of valve 88, a conductor 98 in which a pair of resistors 98 and I88 are inserted, and the heater filament 43 of valve 48 to the supply conductor L. The pairs of heater filaments 8i and 88, and SI and 95, respectively, are illustrated as connected in parallel relation, but it will be readily apparent these pairs of heater filaments may be connected in series relation, if desired, and, as illustrated, the heater filaments 8| and 86 are shunted by a suitable resistor 81.

Direct current anode voltage is supplied both triode sections of valve 18 through a circuit which utilizes the rectifying action of the anode 89 and cathode 98 of valve 88 and which may be traced from the supply conductor L to a conductor I8I, and the anode 89 and cathode 98 of one triode section of valve 88 to one terminal of a condenser I82 which constitutes the positive side of a half wave rectifying unit. The negative terminal of condenser I82 is connected by a conductor I83 to the supply conductor L and, as will be apparent, the condenser I82 operates to smooth out the pulsations in the rectified current flow through the circuit including the anode 89 and cathode 98 of valve 88 which im- -presses a definite constant voltage across its terminals.

As illustrated, the anode I9 of triode A is connected to the positive terminal of condenser I82 through a resistor I83 and the cathode 88 is connected to the negative side thereof. Similarly, the anode 84 of triode B is connected to the positive side of condenser I82 through a resistor I84 and the cathode 85 is connected to the negative terminal of the condenser. The fiow of ripple current through both triode sections of valve 18 is limited to a negligibly small value by operating the valve with the cathodes 88 and 85 virtually cold, the resistor 81 shunting the heater filaments 8i and 88 being provided for this purpose.

It is noted that since individual electrically insulated cathodes are provided for each triode section of valve 88 that it is not necessary to provide means in this arrangement for rendering negligible the effect of variations in the anode current conducted by the triode section including anode 93 on the potentials maintained on the anodes l9 and 84 of valve 18, and furthermore, the full voltage of the supply conductors L and L may be applied to the rectifying unit including the anode 89 and cathode 98.

The output circuit of the triode B is resistance capacity coupled by a resistor I85 and a condenser I85' to the input circuit of the triode section of valve 88 which includes the anode 93. Anode voltage is supplied the latter mentioned triode section directly from the alternating current supply conductors L and L through a circuit which may be traced from the supply conductor L heater filament 43 of valve 48, a conductor I88 in which a resistor I8! is inserted. anode 93, and cathode 94 to the supply conductor L. In order to smooth out the pulsating current fiow through resistor I81 a condenser I88 of suitable value may desirably be connected thereacross. Thus, when an alternating potential in phase with the supply line voltage is impressed on the input circuit of this triode section, the potential drop across resistor I81 will gradually increase in value until a condition of equilibrium is reached, and when an alternating potential out of phase with the supply line voltage is impressed on the input circuit of this triode, the potential drop across resistor I81 will gradually decrease in value.

Thus, a negative potential is built up on the anode 93 which is adapted to be varied as the pick-up coil i1 deflects in one direction or the other from its normally balanced position, and. as in the arrangement of Fig. 1, this negative potential is employed to control the conductivity of valve 48. Valve 48 is connected across the al ternating supply conductors L and L in an inverted position with respect to the manner of connection of the triode section including anode 93 thereacross so that the valve 48 will be conductive during the alternate half cycles when the triode section referred to is non-conductive. As

illustrated, the negative end of resistor I! is connected by a conductor I03 to the control grid 44 of valve 40 and the positive end of resistor I01 is connected through the heater filament 43 to the cathode 42.

. Anode voltage is supplied the valve 40 through a circuit which may be traced from the supply conductor L cathode 42, anode 4|, anda conductor 63, in which a relay 28 and a milliammeter 84 are inserted, to the supply conductor L; The screen grid 45 is desirably maintained at a potential which is somewhat lower than the potential applied the anode Al and as shown may be connected to the point of connection of resistors 99 and I00.

Thus, in this arrangement, as in the arrangement of Fig. .1, the valve 40 is adapted to be alternately rendered conductive and non-conductive and the amplitude of the pulsating current conducted thereby is adapted to be controlled in accordance with the direct current potential drop across resistor I0! which corresponds to the resistor 60 of Fig. 1.

In Fig. 4, I have illustrated, more or less diagrammatically, a modification of a portion of the arrangement disclosed in Fig. 1 in which means are provided for modulating the heat input to the furnace I, that is, supplying heat at a steady rate to the furnace when the temperature is at the desired value and proportionately varying the supply of heat thereto in accordance with the extent of deviation of the temperature from the desired value. This end is obtained in this arrangement by providing feed back means for setting up an oscillation in the amplifier whereby the relay 28 will alternately be actuated to its open and closed position when the'temperature is at the desired value, and as the temperature of the furnace deviates in one sense or the other from the desired value, the period of the oscillation will be varied proportionately so that the interval during which the relay is in its closed position will be varied with respect tothe interval when it will be in its open position. Thus, when the temperature is at the desired value heat will be supplied the furnace at a predetermined rate,-but as the temperature deviates in one sense or the other from this value, the rate of heat supply will be correspondingly varied. This action will be readily distinguished from the action obtained with the arrangement of Figs. 1 and 3 in which on-off action is obtained, that is, the heat supply to the furnace in the device of those figures is either entirely on or entirely oil depending upon whether the temperature of the furnace is above or below the desired value.

Specifically, a resistor H0 is inserted in the conductor 63 in series relation with the relay 28 and the milliammeter 64, the negative end of resistor I Hi being connected to one end of the relay 28 and the positive end being connected to the supply conduceor L through the milliammeter 64. The cathode 3| of valve 29 is connected by a conductor Hi to a contact H2 which is in engagement with and adjustable along the resistor H0. A resistor H3 is inserted in the conductor HI and a connection is provided between the cathode 3| and the supply conductor L which includes a condenser H4.

As will be readily apparent when the valve 40 is rendered conductive the current conducted by this valve will produce-a potential drop across resistor H0, a portion of which, depending upon the adjustment of contact H2 along resistor H0,

is adapted to be fed back into the input circuit of valve 29.

With this arrangement when the temperature of the furnace is at the desired value the pick-up coil I! will be slightly in inductive relation with the field structure I 8 and the sense of this inductive relation is such as to impress a positive potential on the control grid 33 of valve 29 during the half cycles when the anode 35 of valve 34 is positive. Thus, a negative potential will be impressed on the control grid 38 of valve 34 which results in a potential drop acros resistor 60 of such magnitude as to permit the fiow of sufficient current through valve 40 to actuate the relay 28 to its closed position.

' The resulting potential drop produced across resistor III) by the flow of current conducted by valve 48 is in the direction to impress a positive potential on the control grid 33 of valve 29, which potential is superimposed on the alternating voltage impressed thereon by the pick-up coil [1, and causes an oscillation in the anod current conducted by valve 40 of sufllcient magnitude to cause the relay 28 to be intermittently actuated to its open and closed position. As the voltage impressed on the input circuit of valve 29 by the pick-up coil ll increases in one direction or the other, the magnitude of this oscillation is varied in such manner as to cause the relay to remain in its closed position for a longer or shorter period of time with respect to the time in which it is in its open position.

For example, when the controlled temperature falls below the desired value, the voltage impressed on the input circuit of valve 29 by the pick-up coil I! will become more and more predominant over the volta e fed back by the resistor H8 until the latter is ineffective to cause opening of the relay 28, and at intermediate values the feed back voltage will be efiective to cause the relay 28 to be opened for intervals of varying duration depending upon the extent of deviation of the controlled temperature from the desired value. When the temperature is above the desired value the feed back voltage and the voltage induced by the pick-up coil will act in the same direction, that is, to cause opening of the relay 28, and in this case the feed back voltage will be rendered more and more inefiective as the energizing current to the relay 28 is reduced, but the voltage induced in the pick-up coil will be sufiicient to maintain the relay in its open position. At intermediate values the effect of the voltage induced in the pick-up coil to maintain the relay continuously in open position will not be so pronounced and the relay will be actuated to its closed position for shorter and shorter intervals of time as the temperature of the furr'race rises higher and higher above the control point. Thus a proportioning action is obtained which operates to supply varying quantities of heat to the furnace as the temperature deviates about the controlled value.

In Figs. 5 and 6, I have illustrated, more or less diagrammatically, modifications' of a portion of the arrangement disclosed in Fig. 4 for obtaining such proportional control of the supply of heating medium to the furnac I. As illustrated in Fig. 5 feed back means have been provided including a resistor H0 connected in the anode circuit of valve 40, a connection between the cathode 3| of valve 29 and a contact H2 engaging and adjustable along the resistor H0, and a biasing resistor 5 connected between the cathode 3l and the supply conductor L The con- &

nection referred to between the cathode 3i and the contact H2 comprises a conductor iii in which a resistor H6 shunted by a condenser H1 is inserted. The modification illustrated in Fig. 6 includes the resistor H0 and an associated resistor H3 and a condenser H8. As shown the cathcde 31 of valve 29 is connected to the supply conductor L and a connection is provided between the control grid 33 and resistor H0 including the pick-up coil I! (not shown in Fig. 6) a resistor H3 and a contact H2 engaging and adjustable along the resistor H0. Condenser H8 is connected between the left end of resistor H3, as seen in Fig. 6, and the supply conductor L The operation of these modifications is similar to that of the Fig. 4 arrangement for causing an oscillation of the energizing current supplied relay 28 so that the latter will be intermittently actuated to its open and closed position, the duration of the period in which it is in its closed position with respect to the period in which it is in its open position being determined by the extent of deviation of the controlled temperature from the desired value.

While the modifications illustrated in Figs. 4-6 have been illustrated in connection with the amplifier arrangement disclosed in Fig. 1, it will be readily apparent to those skilled in the art that they may be adapted for use with the amplifier arrangement described in Fig. 3. For example, a resistor H0 may be inserted in the conductor 63 between the relay 28 and the milliammeter 64 of this arrangement and a portion of the voltage drop thereacross may be fed back in the manner illustrated in Figs. 4-6 into th input circuit of the triode section of valve 18 which includes the anode l9.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that certain features of .my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. Means for amplifying a voltage including a plurality of electron discharge devices, each of said devices having an input circuit and an output circuit, means to apply said voltage to be amplified on the input circuit of one of said devices, a source of direct current voltage for energizing said one device, means to apply said direct current voltage on the output circuit of said one device, a connection between the output circuit of said one device and the input circuit of a second one of said devices, a condenser in the output circuit of said second mentioned device, a resistor connected across said condenser, means connecting at least a portion of said resistor to the input circuit of a third one of said devices, a source of alternating voltage for energizing said second and third mentioned devices, and means to apply said alternating voltage to the output circuits of said second and third mentioned devices.

2. Means for amplifying a voltage including a plurality of electron discharge devices, each of said devices having an input circuit and an output circuit. means to apply said voltage to be amplified on the input circuit of one of said devices, a source of direct current voltage for energizing said one device, means to apply said direct current voltage on the output circuit of said one device, a connection between the output circuit of said device and the input circuit of a second one of said devices, a condenser in the output circuit of said second mentioned device, a resistor connected across said condenser, a connection including at least a portion of said resistor and the input circuit of a third one of said devices, a-source of alternating voltage for energizing said second and third mentioned devices, and means to apply said alternating voltage to the output circuits of said second and third mentioned devices, said resistor being of such a value in relation to the values of the other elements of said amplifying means that upon change in the voltage of said alternating voltage source the current conducted by said third mentioned device will remain substantially constant.

3. Amplifying means including in combination, a plurality of electron discharge devices, each of said devices having an input circuit and an output circuit and adapted to be energized from a source of alternating supply voltage wherein changes in said voltage affect the output current of said amplifying means, means for so connecting said devices to said source that one of said devices is operative on only one half cycle of said voltage while another of said devices is operative on only the succeeding half cycle, a condenser in the output circuit of said one device, a resistor connected across said condenser, and a connection including at least a portion of said resistor and the input circuit of said other device, said resistor being of such a value in relation to the values of the other elements of said amplifying means that upon change in the voltage of said source the current conducted by said other device will remain substantially constant.

4. Means for amplifying a voltage including a plurality of electron discharge devices, each of said devices having an input circuit and an output circuit, means to apply said voltage to be amplified on the input circuit of one of said devices, a source of direct current voltage applied to the output circuit of said device, a connection between the output circuit of said device and the input circuit of a second one of said devices, a resistor connected in the output circuit of said second mentioned device, a capacitance connected across said resistor, a connection including at least a portion of said resistor and the input circuit of a third one of said devices, a

' source of alternating voltage for energizing said second and third mentioned devices, and means connecting said second and third mentioned devices to said alternating voltage source in inverse manner with respect to each other, said resistor being of such a value in relation to the values of the other elements of said amplifying means that upon change in the voltage of said alternatmg voltage source the current conducted by said third mentioned device will remain substantially constant.

5. Means for amplifying an alternating voltage including a direct current voltage supply source, an electronic valve having an anode, cathode and a control grid, said electronic valve having an output circuit including said anode and cathode and an input circuit including said cathode and control grid, means to apply said direct current voltage between the anode and cathode of said valve, means to apply said alternating voltage circuit of said first mentioned valve to the input circuit of said second mentioned valve including a resistance connected between the anode of said first mentioned valve and the cathode of said second mentioned valve, a condenser connected between the anode of said first mentioned valve and the control grid of said second mentioned valve, and a resistance connected between the cathode and control grid of said second mentioned valve.

WALTER P. WILLS. 

